In general, when a sheet material such as textile fabric is shaped into sewing parts, the cutting is performed based on a paper pattern or on the data corresponding to the paper pattern. A cutting machine or the like used for the cutting has a sharpening function to keep sharpness of a cutting blade for cutting the sheet material (Cf. Patent Citation 1, for example). The Patent Citation 1 discloses a sheet material cutting machine for cutting the sheet material with a cutting knife which is moved in reciprocation along a vertical axis line and also discloses two different ways of sharpening the cutting knife from both sides of its cutting edge.
FIG. 10 shows those two different concepts on the sharpening disclosed by Patent Citation 1. FIG. 10(a) shows one concept on the sharpening with a rounded surface around the outside of a rotary whetstone disclosed in its FIG. 11 and the like. FIG. 10(b) shows another concept on sharpening with a flat surface of the rotary whetstone perpendicular to an axis thereof disclosed in its FIG. 13 and the like. In the following, the simplified construction is illustrated, for explanatory convenience. Although names and reference numerals of parts may vary, the correspondence relation to the two different concepts on the sharperning should be obvious.
In FIG. 10(a), one side 1b of the cutting edge 1a of the cutting knife 1 and the other side 1c of the same are ground with cylindrical surfaces 2a, 3a of outer peripheries of two rotary whetstones 2, 3, respectively. The two rotary whetstones 2, 3 are supported at front ends of two arms 4a, 4b of a support block 4. The two arms 4a, 4b are fixed with spaced apart from each other at a certain angle. The support block 4 can be pivoted about or swung and displaced around a pivot shaft 5 penetrating intermediate portion between the arms 4a, 4b. When the support block 4 is pivotally displaced with respect to the pivot shaft 5 in one direction or the other, the one side 1b of the cutting knife 1 or the other side 1c of the same can be ground with the related cylindrical surface 2a, 3a of the rotary whetstone 2, 3. In this regard, however, since the sharpening is performed using the cylindrical surface 2a, 3a, even when one side 1b and the other side 1c of the knife 1 initially have a linear cross-sectional shape, they are varied in cross-section to have a concave surface, as shown as a shaded area.
In FIG. 10(b), like reference numerals are labeled to corresponding parts to FIG. 10(a), to avoid redundant explanation. In the support block 4, the arms 4a, 4b mount the rotary whetstones 2, 3 on the sides facing the cutting edge 1a of the cutting knife 1, respectively. Although the rotary whetstones 2, 3 are away from the cutting knife 1 in the full-line state, they can be switched to the state in which the flat surfaces 2b, 3b perpendicular to the rotation shafts are put in contact with the one side 1b and the other side 1c of the knife 1, respectively, to sharpen them. For example, when the support block 4 is pivotally displaced in one direction with respect to the pivot shaft 5, the flat surface 2b of the rotary whetstone 2 is switched to the state of being put in contact with the one side 1b of the cutting knife 1 to sharpen it. Likewise, when the support block 4 is pivotally displaced in the other direction with respect to the pivot shaft 5, the flat surface 3b of the rotary whetstone 3 is switched to the state of being put in contact with the other side 1c of the cutting knife 1 to sharpen it. As the cutting knife 1 is ground with the flat surfaces 2b, 3b, the linear cross-sectional shape of the cutting knife 1 is kept unchanged, as shown as the shaded area.
In the sharpening way shown in FIG. 10(a), the cylindrical surfaces 2a, 2b of the rotary whetstones 2, 3 can be put in contact with the one side 1b of the cutting edge 1a of the cutting knife 1 and the other side 1c of the same, respectively, via a link mechanism and the like, not via an overall pivotal displacement of the support block 4 (Cf. Patent Citation 2, for example). According to Patent Citation 2, the rotary whetstones 2, 3 and the whetstone supporting structure are contained in the rotary cylinder which is turned around an R-axis as a rotation shaft of the cutting edge of the cutting blade equivalent to the cutting knife 1. The switching between the sharpening states is performed by turning the rotary cylinder while locking the rotation ring mounted on the rotary cylinder to be stationary relative to outside. A relative angular displacement between the rotation ring stationary with respect to outside and the rotary cylinder able to turn with respect to outside allows the rotary whetstones to pivotally displaced separately via the cams and the link mechanism, thereby allowing the switching between the sharpening states.    Patent Citation 1: JP Patent Publication No. Sho 56-8759    Patent Citation 2: JP Patent No. 3390219